Remanent magnetization in CoO antiferromagnetic nanoparticles

8 páginas, 7 figuras, 1 tabla.-- PACS number(s): 75.30.Cr, 75.50.Ee, 75.50.Tt.-- et al.We report a study on the remanent magnetization Mr induced by field cooling across the ordering temperature TN in antiferromagnetic CoO nanoparticles with different sizes. The nanoparticles are composed by a structurally and magnetically ordered core and a structurally ordered and magnetically disordered shell with a thickness of about 2 nm. The ordered core has cell parameters, moments direction, and modulus similar to those of bulk CoO. Mr is shown to be proportional to the cooling field Hcool. The low-temperature saturation values of Mr [Mr(0)] in the CoO nanoparticles are about two orders of magnitude higher than those found for bulk CoO. Mr/Mr(0) of CoO nanoparticles scales with temperature in a single curve, independently on the magnitude of Hcool and on nanoparticles size, except for temperatures near to TN since TN is size dependent.The Aveiro-Zaragoza collaboration has been supported by the Integrated Spanish-Portuguese Action under Grant No. PT2009-0131. The work in Zaragoza has been supported by the research Grants No. MAT2007-61621, No. MAT2009-13977-C03-01, and No. CONSOLIDER CSD2007-00010 from the Ministry of Education. N.J.O.S. acknowledges CSIC for a I3P contract and FCT for Ciencia 2008 program.Peer reviewe